The traditional measuring device for woodworkers and carpenters is the folding rule. Modern versions of these time-honored tools are made of wood, metal or plastic and come in two types: the four-fold rule in 2- or 3-ft. lengths, and the zig-zag style that usually opens to 6 ft. Folding rules are compact (6 to 8 in. long when closed) and rigid enough to span long distances without drooping. If you’re in the market for a folding rule, buy one with a caliper extension built into the first blade for taking inside measurements (See Photo, right).
One-piece rules, available in lengths ranging from 6 in. to 3 ft., are indispensible in the shop. Six-in.-long pocket rules typically come with a narrow, flexible blade and a sliding-“T” cross-member for taking depth measurements and setting machine blade and bit heights. The longer bench rules serve a variety of uses including general measuring and setting instruments such as a compass or dividers. They also can be used as a straightedge guide. Every shop needs at least a 12-in. and a 24-in. rule. Purchase these rules as interchangeable blades for your combination square to make your rules even more versatile. Rules are available with metric and standard graduations. A handy combination for standard is 1/8- and 1/16-in. increments on one face and 1/32- and 1/64-in. markings on the other.
Four ways to take an inside measure.
1: Extend a tape measure and add the length of the case to the measurement on the tape.
2: Using a folding rule with a caliper extension, unfold the rule then extend the caliper out the remaining distance. Add the lengths of the rule and caliper.
3: Lay a metal rule and tape measure together, then add the measurements indicated.
4: Lay two pieces of scrap wood together and draw a reference mark across both scraps where they intersect. Remove the two scraps, realign the marks and measure the combined length.